Mechanisms underlying viral persistence in the course of AIDS remain one of the more perplexing aspects of HIV-1 pathogenesis at the present time. The chronic nature of AIDS is reflected by the ability of the virus to be maintained in a minimally replicative state without inducing rapid host cell cytolysis. These facts are difficult to reconcile given the properties of HIV-1 in vitro where infection of host CD4 cells results in rapid cytolysis and high level virus replication, thus mechanisms which restrict or regulate virus replication play an important role in the pathogenesis of AIDS. Our studies demonstrate two mechanisms of central importance in maintenance of a persistent viral state in AIDS: 1. The emergence of non-cytopathic HIV-1 genotypes which are able to persist within the host cell. 2. The activated state of the host CD4+ lymphocyte. Specific Aim A: Evaluate resting CD4+ T-lymphocytes as an HIV-1 reservoir in AIDS. (I).Determine ability of HIV-1 to replicate in resting CD4 cells in vitro. (II). Identify T-cell subset which harbors HIV-1 DNA in vivo and examine state and load of a proviral DNA in AIDS patients. (III) Evaluate opportunistic agents for ability to augment HIV-1. production from resting T-cells in vitro. Specific Aim B: Identify the presence of noncytopathic HIV-1 genotypes in AIDS patients which contribute to viral persistence.(I) Clone noncytopathic viruses from HIV-1 seropositive individuals. (II). Through the construction of chimeric viruses and DNA sequencing, delineate regions of the genome which are important for the noncytopathic phenotype. It is proposed that these studies will provide fundamental insight into the basis for viral persistence in AIDS and identify biologic features of the host cell reservoir and of the virus itself which effect maintenance of the virus in this reservoir.